Microporous and Mesoporous Carbon Xerogel Having a Characteristic Mesopore Size and Precursors Thereof and Also a Process for Producing These and Their Use

Abstract

The invention relates to a microporous and mesoporous carbon xerogel and organic precursors thereof based on a phenol-formaldehyde xerogel. A characteristic parameter common to carbon xerogels is a peak in the mesopore size distribution determined by the BJH method (Barrett-Joyner-Halenda) from nitrogen absorption measurements at 77 K in the range from 3.5 nm to 4 nm. The production process is characterized firstly by the low starting material costs (use of phenol instead of resorcinol) and secondly by very simple and cost-effective processing; convective drying without solvent exchange instead of supercritical drying or freeze drying. The carbon xerogels and their organic phenol-formaldehyde xerogel precursors have densities of corresponding to a porosity of up to 89%, and the xerogels can also have a relevant mesopore volume. The carbon xerogels obtained from the phenol-formaldehyde xerogels are also microporous.

1 . A mesoporous phenol-formaldehyde xerogel, wherein said mesoporous phenol-formaldehyde xerogel can be dried under standard conditions without exchange of solvent. 
     
     
         2 . The phenol-formaldehyde xerogel as claimed in  claim 1 , wherein said mesoporous phenol-formaldehyde xerogel is pyrolyzed after drying and thus converted to a carbon xerogel. 
     
     
         3 . The carbon xerogel as claimed in  claim 2 , wherein said carbon xerogel has a clearly identifiable peak in the pore size distribution by the BJH method (Barrett-Joyner-Halenda; DIN 66134) between 3.5 nm and 4.0 nm from measurements with nitrogen sorption at 77 K. 
     
     
         4 . The carbon xerogel as claimed in  claim 3 , wherein said carbon xerogel is present in granule or powder form after a further treatment. 
     
     
         5 . A process for producing a carbon xerogel, wherein a hydroxybenzene excluding resorcinol (1,3-dihydroxybenzene), especially monohydroxybenzene, 2,6-dimethylphenol, 2,4-di-tert-butylphenol and mixtures thereof, and formaldehyde gelate in a sol-gel process to give a wet phenol-formaldehyde gel, and then the wet gel is dried convectively at temperatures of 0° C.-200° C. 
     
     
         6 . The process as claimed in  claim 5 , wherein the catalyst used is an acid or a base, especially hydrochloric acid (HCl) or sodium hydroxide (NaOH). 
     
     
         7 . The process as claimed in  claim 5 , wherein the solvent is water, a ketone or an alcohol, especially n-propanol. 
     
     
         8 . The process as claimed in  claim 5 , wherein the gelation is effected at temperatures of 20-120° C. 
     
     
         9 . The process as claimed in  claim 5 , wherein there is no solvent exchange. 
     
     
         10 . The process as claimed in  claim 5 , wherein the molar phenol to catalyst ratio P/C is between 0.1 and 30. 
     
     
         11 . The process as claimed in  claim 5 , wherein the molar formaldehyde to phenol ratio F/P is between 0.5 and 20. 
     
     
         12 . The process as claimed in  claim 5 , wherein the proportion by mass M of the phenol and formaldehyde reactants in the overall solution is between 5% and 60%. 
     
     
         13 . The process as claimed in  claim 5 , wherein the PF xerogel is carbonized at more than 600° C. under a protective gas atmosphere. 
     
     
         14 . The process as claimed in  claim 13 , wherein the carbon xerogel is activated at more than 500° C. with an oxygenous gas or a salt melt, or at a temperature below 200° C. with an acid or a base. 
     
     
         15 . The process as claimed in  claim 5 , wherein the monolithic xerogel is comminuted into granules or powder, for example by the action of mechanical forces as in grinding. 
     
     
         16 . The use of a xerogel corresponding to  claim 1  as thermal insulation, an IR adsorber, a catalyst support, a filter, or as an electrode in supercapacitors, fuel cells or secondary cells, or for fluid or gas separation, or in sensor technology, or as an electrically and thermally conductive component in composites, or composite component in fiber-reinforced materials, or as casting molds for melts. 
     
     
         17 . The use of a xerogel produced in  claim 5 , as thermal insulation, an IR adsorber, a catalyst support, a filter, or as an electrode in supercapacitors, fuel cells or secondary cells, or for fluid or gas separation, or in sensor technology, or as an electrically and thermally conductive component in composites, or composite component in fiber-reinforced materials, or as casting molds for melts.